Low noise back pressure regulator for supercritical fluid chromatography

Abstract

A drive mechanism for back pressure regulator used in liquid chromatography, supercritical fluid chromatography, or supercritical fluid extraction allows very fine automated control over a very wide range of pressures by combining a linear actuator compressing a spring, pushing a pin. The nozzle assembly of the regulator comprises a flow through chamber containing a diaphragm and a seat, in which the pin pushes the diaphragm against the seat, together with an upstream pressure sensor and electronic feedback control to the motor of the actuator. The BPR of the embodiments exhibits high pressure stability and extremely low pressure noise, even at moderate to high pressures. The exemplary BPR can be use at either constant pressure or to generate pressure programs where the pressure is varied versus time. Further, the nozzle assembly has a field-replaceable head, requiring no mechanical adjustment on replacement.

What is claimed is: 
     
       1. A device for a back pressure regulator, comprising:
 a nozzle insert comprising; 
 an outlet flow channel that can receive an outlet flow tube and an inlet flow channel that can receive an inlet flow tube; 
 a seat, near an end of said insert, such that said seat can be in fluidic communication with said outlet flow channel; and 
 a nozzle body at least partially receiving said nozzle insert and said seat; and a diaphragm having a first surface positioned adjacent to said seat wherein said nozzle body constrains a circumferential edge of said diaphragm. 
 
     
     
       2. The device of  claim 1 , wherein said outlet flow channel is located near to center axis of said nozzle insert, and said inlet flow channel is located at a position offset from said outlet flow channel. 
     
     
       3. The device of  claim 1 , further comprising:
 a heating element arranged near to said outlet channel such that heat from said heating element can be in thermal communication with said outlet flow channel. 
 
     
     
       4. The device of  claim 1 , further comprising:
 a shim element, positioned adjacent to a second surface of said diaphragm that is opposite to said first surface of said diaphragm that is adjacent to said seat. 
 
     
     
       5. The device of  claim 1 , further comprising:
 a linear actuator that can apply a force to the second surface of said diaphragm directly or through said shim, wherein said force can cause the first surface of the diaphragm to seal against an orifice of said seat. 
 
     
     
       6. The device of  claim 5 , wherein the linear actuator comprises a motive force driving a spring element: and a thrust element, driven by said spring element, can apply said three to said diaphragm. 
     
     
       7. The device of  claim 6 , wherein said motive force comprises a positional control that can move said linear actuator in displacement steps related to a pressure change in said inlet flow channel or said outlet flow channel. 
     
     
       8. A process for regulating back pressure in a chromatography system with the device of  claim 1 , comprising:
 pumping a pressurized fluid flowstream into a nozzle insert via a nozzle inlet channel; 
 directing said fluid from said inlet channel into a seat of said insert; 
 positioning a diaphragm adjacent to said seat to seal an outlet channel of said nozzle insert; 
 constraining said diaphragm with a nozzle body; 
 deflecting the diaphragm away from said seat with said pressure of said pressurized fluid flowstream thereby allowing the flow stream to increase flow into an outlet channel of said nozzle insert; 
 applying an opposing deflection force to said diaphragm thereby causing the flowstream to decrease flow into the outlet channel. 
 
     
     
       9. The process of  claim 8 , further comprising:
 heating the outlet flowstream with a heating element that is in thermal communication with said outlet flow channel. 
 
     
     
       10. The process of  claim 8 , wherein said applying the opposing deflection force further comprises applying said opposing force with a spring shim positioned adjacent to a surface of said diaphragm that is opposite to a side adjacent to said seat. 
     
     
       11. The process of  claim 10 , wherein said applying the opposing deflection force further comprises applying a motive force to a thrust element with, the thrust element then applying a force to the shim, said motive force actuated in displacement steps related to a pressure change in one of said flow channels. 
     
     
       12. The process of  claim 10 , wherein the pumping the pressurized fluid flowstream further comprises pumping said flowstream in a supercritical fluid chromatography system or a high performance, liquid chromatography system.